TOC measurement of organic matter included in sample water containing few impurities, such as water for manufacturing pharmaceuticals, process water for semiconductor manufacturing, cooling water, boiler water, or tap water, is performed for the purpose of managing such kinds of water.
A instrument that measures a TOC concentration of sample water while keeping the sample water in the liquid phase has also been developed as a TOC measurement instrument. In the case of such a TOC measurement instrument, while keeping sample water in the liquid phase, organic matter contained in the sample water is oxidized to carbon dioxide by being subjected to ultraviolet light irradiation at an oxidative decomposition unit, and thereafter is introduced into a carbon dioxide separation unit. At the carbon dioxide separation unit, a sample water channel and a measurement water channel, through which measurement water flows, are brought into contact through a gas permeable membrane, and thus carbon dioxide contained in the sample water is transferred to measurement water. The measurement water into which carbon dioxide has been transferred is sent to a conductivity measuring unit to measure the conductivity thereof. By previously determining a calibration curve representing the relationship between the conductivity of measurement water and the carbon dioxide concentration of sample water, it is possible to determine the carbon dioxide concentration of the sample water based on the measured conductivity of the measurement water (see Patent Literature 1).
In the case of such a TOC measurement instrument, a liquid feeding device that drives a syringe using a ball screw is used as a liquid feeding device for feeding sample water. Further, in some cases a liquid feeding device that drives a syringe using a ball screw is also used as a liquid feeding device that supplies measurement water to the conductivity measuring unit. In a liquid feeding device of this kind, a ball screw is used as a linear feed mechanism. Rotation of the ball screw is driven by a pulse motor to thereby control the flow rate for injecting sample water or feeding measurement water. In this connection, in some cases feeding of liquid is controlled by means of the flow velocity instead of the flow rate. Although control of liquid feeding by means of the flow rate is described hereunder, the present invention also includes a case in which liquid feeding is controlled by means of the flow velocity instead of the flow rate.